Fluid filter and methods for making same

ABSTRACT

A filter having a substantially cylindrical or slightly tapered body design which has a plurality of elongated apertures formed therethrough. Each aperture is defined side to side by a pair of elongated, wedge-like rib members disposed one on each side of each aperture, and top to bottom by a pair of cross members which present a substantially square top side and an angularly declining bottom side. The end effect is a substantially rectangular entry aperture for fluid flow with the exception of the declining bottom side which promotes smooth, low resistance entry flow. The present invention is also directed to a method of manufacture of filters having the above-described characteristics. In particular, the preferred method involves an injection molding process in which a molten plastic (such as high-density polyethylene, HDPE) is injected into a two-part mold. The mold generally comprises a smooth, substantially cylindrical cavity and a notched and grooved core which is inserted into the cavity in a partial surface to surface contact relationship to complete the filter mold. Due to the extremely close tolerances required by a such a core and cavity surface to surface relationship, unique mold alignment modifications were also developed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to fluid filters and moreparticularly to a filter which has distinctive inlet apertures defined,in part, by angularly declining surfaces. This invention further relatesparticularly to methods for making such filters. Filters of thisinvention present a distinct advantage in extracorporeal blood systems.

BACKGROUND OF THE INVENTION

[0002] Fluid filters come in many shapes and sizes depending primarilyon their intended usage. For example, filters positioned at the inlet toa pipe or tubing system are often also tubular in form. Conical andtapered cylindrical forms are alternatives used in these situations aswell. Aperture size and quantity may also drive the ultimate geometricshape chosen for use. So too may the fluid to be filtered.

[0003] An example of a fluid system having special requirements whichcan be significantly impacted by filter shape is a blood flow systemoutside the body, i.e., an extracorporeal blood system. Poor flowpatterns can create problems for blood flowing through an extracorporealblood system. Excessively turbulent or unduly slowed or stagnated bloodflow may activate the blood's clotting processes causing the formationof blood clots and strands in the blood. Clotting of blood in anextracorporeal blood system may result in occlusion of the tubing linesor in injury to the patient.

[0004] Extracorporeal blood systems usually include devices commonlyknown as drip chambers or bubble traps (referred to herein generally asbubble traps). One purpose of such devices is to capture and removepotentially harmful elements (such as air bubbles or blood clots) fromthe blood prior to treating the blood or returning it to the patient.Filters are often used to assist in this removal, particularly forcatching blood clots and other particulates. A typical filter of thistype is a conical or cylindrical device having numerous perforationsformed therein. Examples of such filters can be found used in the bubbletraps disclosed in the U.S. Patents to Brugger (U.S. Pat. Nos. 5,503,801and 5,591,251) and Raabe et al. (U.S. Pat. No. 5,489,385). A bubble trapwith a filter of this type is also commonly incorporated into andthereby forms a distinct part of a cartridge cassette of anextracorporeal blood tubing and cartridge set such as those disclosed inthe U.S. Patents to Heath et al. (U.S. Pat. Nos. 4,666,598 and4,770,787), inter alia.

[0005] It is believed that numerous filter designs may promote bloodclotting because, among other possible detriments, they present aninherent resistance to ordinary blood flow. Resistance in a blood flowpath slows the blood's progress which, in turn, allows the blood toinitiate clotting. Such clotting can occur at points of stagnation oralong surfaces presenting a high degree of frictional resistance.Resistance may also cause turbulence in blood flow filters and is thussought to be avoided here as well. Turbulent blood flow may lead toclotting or the formation of air bubbles in the blood. If returned tothe patient in the blood, either of these present a risk of adversehealth consequences to the patient.

[0006] Though still operable for passing blood, filters of the prior artnevertheless suffer geometric inefficiencies which present friction,stagnation and/or general slowing of the blood flow; any of whichconditions possibly leading to blood clotting. For instance, the filtersin the bubble traps of Brugger '801 and '251 (referred to above) presenta plurality of substantially square, right-angled entry windows (incross-section) which force the generally downwardly flowing blood inthose bubble traps to make right-angled turns in order to enter therespective filters. Such right-angled turns can have the effect ofslowing the blood flow as well as creating stagnation points at thelines of flow divergence. The filter designs of Raabe et al. '385 suffersimilar geometrical, flow-impairing drawbacks. The filters shown inRaabe have external projections which also force substantially rightangled flow redirections for entry of blood into those filters. It isthought that such redirections cause slowing and stagnation which maypromote clotting and thereby, flow restrictions.

[0007] Thus, it is apparent that there remains a distinct need forcontinued improvements in blood flow filters which effectively removesolids from the blood yet provide unhindered passage of the bloodtherethrough. It is toward this end that the present invention isdirected.

SUMMARY OF THE INVENTION

[0008] The filter of the present invention has a substantiallycylindrical or slightly tapered body design which has a plurality ofelongated apertures formed therethrough. Each aperture is defined sideto side by a pair of elongated, wedge-like rib members disposed one oneach side of each aperture. and top to bottom by a pair of cross memberswhich present a substantially square top side and an angularly decliningbottom side. The end effect is a substantially rectangular entryaperture for fluid flow with the exception of the declining bottom sidewhich promotes smooth, low resistance entry flow.

[0009] The present invention is also directed to a method of manufactureof filters having the above-described characteristics. In particular,the preferred method involves an injection molding process in which amolten plastic (such as high-density polyethylene, HDPE) is injectedinto a two-part mold. The mold generally comprises a smooth,substantially cylindrical cavity and a notched and grooved core which isinserted into the cavity in a partial surface to surface sealing contactrelationship to complete the filter mold. Due to the extremely closetolerances required by a such a core and cavity surface to surfacesealing relationship, unique mold alignment modifications were alsodeveloped.

[0010] These and other features of the present invention will be furtherilluminated in the following detailed description read in conjunctionwith the accompanying drawings which are described briefly below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a side elevation of a filter of the present invention;

[0012]FIG. 2 is a cross-sectional view of a portion of the filter ofFIG. I taken from the circled area 2 thereof;

[0013]FIG. 3 is an isometric view of the filter of FIG. 1;

[0014]FIG. 4 is an enlarged view of the portion inside circled area 4 ofFIG. 3;

[0015]FIG. 5 is a bottom plan view of the filter of FIG. 1;

[0016]FIG. 6 is an enlarged, isometric. substantially two-thirds view ofthe interior of the filter of FIG. 1 taken from the circled area 6thereof;

[0017]FIG. 7 is a generalized illustration related to the filter ofFIGS. 1-6 showing fluid flow therethrough;

[0018]FIG. 8 is a generalized illustration showing fluid flow through afilter of the prior art;

[0019]FIG. 9 is another generalized illustration showing fluid flowthrough yet another filter of the prior art;

[0020]FIG. 10 is a perspective view of the filter of the presentinvention shown disposed for use inside a partially broken-awayextracorporeal blood bubble trap chamber;

[0021]FIG. 10A is a cross-sectional view of the filter and bubble trapchamber of FIG. 10 taken along line A-A thereof showing the flow offluid therethrough;

[0022]FIG. 11 is a side elevation of the filter of the present inventionshown disposed for use inside a cartridge blood processing system;

[0023]FIG. 12 is a broken, partially side elevational, mostlycross-sectional view of a core pin used during injection molding of thefilter of the present invention;

[0024]FIG. 12A is a bottom plan view of the core pin of FIG. 12 takenalong line A-A thereof;

[0025]FIG. 12B is a cross-sectional view of the core pin of FIG. 12taken along line B-B thereof,

[0026]FIG. 13 is a cross-sectional view of a cavity into which the corepin of FIG. 13 is disposed during injection molding of a filter of thepresent invention;

[0027]FIG. 113A is a cross-sectional view of the cavity of FIG. 13 takenalong line A-A thereof;

[0028]FIG. 14 is a cross sectional view of the core and cavity of FIGS.12 and 13 in operative molding position relative to each other and aninjection nozzle and base;

[0029]FIG. 15 is an exaggerated, schematic view of a core and filterillustrating the ejection technique used to remove the filter from thecore;

[0030]FIG. 16 is a schematic view of an alternatively shaped core for anejection technique comparison relative to FIG. 15:

[0031]FIG. 16A is a generalized flow diagram for the filter resultingfrom the alternatively shaped core of FIG. 16;

[0032]FIG. 17 is a cross-sectional schematic view of the principalelements involved in the injection molding operation of the presentinvention; and

[0033]FIG. 18 is a schematic, partially broken-away, isometric view ofthe molding apparatus of the present invention.

DETAILED DESCRIPTION

[0034] The present invention is directed to a filter which is shown inthe attached drawings and identified generally by the reference numeral20. In particular and as shown primarily in FIGS. 1 and 3, filter 20comprises a hollow, substantially cylindrical or tubular body portion 22which has at its open lower end 24 a flange 26 and at its closed upperend 28 a header 30. Defined in and through body portion 22 are aplurality of apertures 32 through which the fluid to be filtered passeswhen filter 20 is in use. Note, while in use, fluid is intended to flowfrom the exterior of filter 20 to its interior open area identifiedgenerally by the reference numeral 34 in FIGS. 3 and 5, for example.

[0035] As shown in more detail in FIGS. 24, apertures 32 are defined bylongitudinally extending rib members 36 and by declining, fillet-typecross portions 38. As viewed in FIGS. 2-4, the rib members 36 and thecross portions 38 may appear to be separate entities, however, they areinstead integrally formed during the injection molding process to bedescribed below. The exterior view of filter 20 shown in FIGS. 1 and 3better shows the integrality of rib members 36 and cross portions 38.

[0036] As can be seen from FIGS. 3-5. but still more particularly inFIG. 6. the elongated rib members 36 are substantially prismaticwedge-shaped members each having a relatively narrower nose portion 35and a relatively wider base 37. The respective nose portions 35 of eachof the wedges are faced inwardly toward the open interior 34 of thefilter 20. Rib members 36 preferably have substantially isoscelestriangularly shaped cross sections with convexly-rounded bases 37corresponding to the external curvature of body 22. The two base anglesα (alpha) of the isosceles triangles are substantially equal to eachother as well as being substantially equal for all ribs 36. Similarly,the respective nose angles β (beta) are substantially equal to eachother. Note, the sizes of the nose angles β are related to the sizes andquantities of apertures 32 desired for use in a filter 20. Angles β ofbetween about 60 and about 90 degrees have been found practical althoughboth smaller and larger angles will also be effective. Angles β ofbetween about 80 and 85 degrees are currently preferred. Each of thenose portions 35 may, as shown, also be convexly-rounded, oralternatively concavely-rounded depending primarily on the method ofmanufacture (as this is described in more detail below). Also as shownin FIGS. 3-5, but more particularly in FIG. 6, the declining crossportions 38 are also substantially prismatic, here having substantiallyright triangularly shaped cross sections. Respective interior angles κ(kappa) and λ (lambda) are shown in FIG. 6 for the right triangular.cross sectional views of two exemplary cross portions 38. The angles κof all the cross portions 38 are preferably 20 degrees, although otherangles will also be effective. Note, an angle κ of 20 degreescorresponds generally to a preferred angle ω (omega) of about 70 degreesdown from the horizontal. Angle ω thus defines the preferred angle ofdeclination of faces 40 from the horizontal.

[0037] Cross portions 38 provide significance for filter 20 throughtheir declining faces 40 as shown best in FIG. 6. These faces 40 furnishthe distinct advantage of low resistance to the flow of the fluid as itenters filter 20. As shown by the flow arrows in FIG. 7, fluid entersthe apertures 32 of filter 20 at an ever downward, albeit angular,orientation. In comparison. as shown by FIGS. 8 and 9, filters of theprior art present a substantially horizontal redirection of the entryflows therein. Note. filter 20A of FIG. 8 substantially represents thefilters shown and described in the Brugger patents '801 and '251, andfilter 20B of FIG. 9 substantially represents the cylindrical filters ofRaabe '385. Raabe does have declining faces 21B on the undersides of theexternal cross portions 23B thereof; however. due to the injectionmolding process thereof which specifically involves external shaping (asdescribed below), a forced horizontal inlet flow is inescapable.

[0038] Before examining the respective manufacturing processes indetail, please refer to FIGS. 10 and 10A, in which a filter 20 of thepresent invention is shown in an exemplary use inside a bloodcirculating bubble trap chamber 50. Note that flange 26 is used tosecure filter 20 in place within chamber 50. To do so, flange 26 willhave a diameter wider than the diameter of the collar 52 of the chamberoutlet/exit port 54. Thus, filter 20 is inserted in the outlet 54 and isdisposed such that the body 22 and header 30 are fully, or substantiallyfully, positioned within the lower portion 55 of chamber 50. Flange 26of filter 20 remains outside chamber 50 since it is wider than collar52. An exit coupling 56 surrounds the exit port 54 and receives theflange 26 of filter 20 and also receivably retains exit conduit 60. Theexit conduit 60 is frictionally engaged by and preferably solvent bondedto the exit coupling 56 with the filter flange 26 sandwiched between theexit conduit 60 and collar 52 thereby preventing dislocation of filter20 and exit conduit 60 during extracorporeal treatment.

[0039] In operation, blood flows into chamber 50 through an inletconduit 62 to an upper portion 64 of chamber 50. The blood flowsdownwardly toward the chamber outlet 54. Here, the blood flows throughfilter 20. out the exit port 54 and into and through exit conduit 60ultimately back to the patient (not shown).

[0040] Use with the bubble trap 50 of FIGS. 10 and 10A is, again,exemplary. Another exemplary use is inside a fluid flow cassette asdisclosed in the U.S. patents to Heath et al. (U.S. Pat. Nos. 4,666,598and 4,770,787), inter alia. The use of a filter 20 in such a device isshown schematically in FIG. 11. In much the same way blood entered thebubble trap 50 of FIGS. 10 and 10A, blood enters the filtering chamber92 of cassette 90 through an inlet 94 (though from the bottom right inthis example), and then flows through the chamber 92 downwardly tofilter 20. The blood then enters the filter 20 and finally exits thecassette system through exit aperture 96. The blood then flows back tothe patient (not shown) through an outlet conduit 98. The other portionsof cassette 90 which are shown but not discussed are understood in theart as described in Heath et al. '598 and '787.

[0041] Also, entry aperture size and quantity is dictated somewhat bythe pressure drop/head loss, and chamber outlet size as well as by thefluid to be filtered. It is thus, for example, preferred that the totalinlet area of the totality of apertures 32 be greater than the outletarea(s) presented by either of the outlets 54 or 96 shown in FIGS. 10and 11, respectively. Therefore, given an outlet area then, thepreferred number and sizes of apertures can be determined, with a ratioof size to total number giving some alternatives. Extracorporeal bloodwill also require a maximum aperture size. Thus, a maximum size peraperture will then dictate an overall number of apertures which, inturn, will dictate a minimum length and or width of a body 22.Similarly, aperture width in a filter of the above-described type, willalso impact the wedge angle of the elongated ribs 36. Narrower aperturewidths will usually require wider wedge angles (or more aperturescircumferentially). Note, aperture sizes having 1.5 mm heights and from0.20 to 0.35 mm widths have been found operable with less pressure dropsthan the prior art filters of Brugger and Heath et al. (502 mnmHgaverage pressure drop of 10 prior art filters; compared to 433, 430, and427 mmHg average pressure drops of 10 each of 0.20, 0.28 and 0.33aperture width filters of the present invention).

[0042] Filter 20 is preferably constructed of substantially flexibleHDPE (high-density polyethylene) using an injection moldingmanufacturing technique to be further described below. Flexibilityallows for this particular part to be simply molded in that it allowsfor the core of the mold to be easily pulled from the finished filtereven though there is some overlap of the filter on and within notches inthe core. HDPE is also preferred because HDPE is biocompatable and bothgas and gamma-sterilizable and is thus suitable for use inextracorporeal treatment systems through which blood will pass. Othermaterials are also foreseeably usable herewith. For example.polypropylene, polyvinyl chloride (PVC), linear low-density polyethylene(LLDP). or any polyolefin providing soft PVC rubber-like characteristicsmay be used in this invention.

[0043] In manufacturing a filter 20 of the present invention, thepreferred method involves injection molding high-density polyethylene(HDPE) using primarily a two-part mold. The two parts include a smooth,substantially cylindrical cavity and a notched and grooved core. Thesemold elements are shown in more detail in FIGS. 12 and 13. As can beseen in FIG. 12, core 70, is a generally solid body having a hollowedcylindrical center portion 72 defined therein. Hollow portion 72 is usedto house a knockout pin (not shown in FIG. 12). Core 70 also has aplurality of circumferential notches 74 defined therein which are usedto form the angular, declining faces 40 of cross portions 38. A flat,hollowed conical area 76 is also shown in FIG. 12 at the lower end ofcore 70. Conical area 76 provides the opening used to create header 30of filter 20.

[0044]FIGS. 12A and 12B help further illustrate the distinctive surfaceformations of core 70. In particular, FIG. 12A shows the end view of theelongated grooves 78 which are defined by and between elongated ridges79. Grooves 78 form the mold voids which are used to cast the elongated.wedge-like ribs 36 running the length, top to bottom of the filter 20.Note, these ridges 78 are visible in FIG. 12 only in the sideelevational portion thereof as the cross sectional portion of FIG. 12 istaken through the centers of diametrically opposed ridges 79. as shownby the cross-section defining lines 12-12 in FIGS. 12A and 12B. FIG. 12Bshows a cross-section taken approximately mid notch to show theinterconnection of notches 74 and grooves 78.

[0045]FIGS. 13 and 13A show the cavity portion 80 of the mold of thepresent invention. Cavity 80 is a solid single member having a hollowsubstantially cylindrical opening 82 defined therethrough. Note, thepreferred embodiment of filter 20 is substantially cylindrical yetslightly tapered as shown best by the angle Θ (theta) in FIG. 13. Alldepictions of the preferred embodiments herein are intended to have suchan angle Θ; for example, the core 70 of FIG. 12 is also formed with aninherent angle Θ as is also shown therein. Thus, a slightly taperedfilter 20 will result. (Note, angle Θ is not shown relative to thefilters of the previous FIGS. 1-11, though these filters also preferablyhave a taper defined by such an angle Θ as well.)

[0046] Furthermore, the core 70 of FIG. 12 will fit inside and meetsealingly wall to wall with the interior surface 82 of cavity 80. Morespecifically, each of the faces 84 at the apexes of ridges 79 of core 70will meet wall to wall with interior surface 82. Sealingly means thateach of these faces 84 contacts the interior surface 82 sufficiently sothat the mold material will not be able to enter any space therebetween.Thus, sealingly here does not mean there are any elastic contacts;rather, only face to face contacts. These multiple surface contact areasthus define the ultimate apertures 32 formed in a finished filter 20.This therefore requires very precise machining of the corresponding moldtools; the core 70 and the corresponding cavity 80. Thus, thecorresponding diameters at each contact point must be identical. Morespecifically. the angles Θ of core 70 and cavity 80 are identical.Likewise, diameter d of core 70, as shown at the lower end of the corein FIG. 12, is identical to corresponding diameter d of cavity 80 shownat the lower end of FIG. 13. Similarly, diameter d′ at any height ofcore 70 must be identical to the d′ at the corresponding height ofcavity 80. Diameters d″ at the corresponding top portions of core 70 andcavity 80 are thus also identical. This correspondence is shown in moredetail in FIG. 14, where the core 70 is shown disposed inside the cavity80. The interior surface 82 of cavity 80 is preferably diamond polishedso that the exterior surfaces of resulting filters 20 will be as smoothas possible. thereby presenting still less resistance to fluid flow.

[0047] Referring now specifically to FIG. 14, this shows the closedposition in which the core 70 is disposed inside the cavity 80 for theactual molding of a filter 20. Note, flange 26, several cross portions38 and the header 30 of a filter 20 are the only visible portions offilter 20 in this cross section. Note also the abutment of the exteriorfaces 84 of core 70 with the interior face 82 of cavity 80.

[0048] There are two additional. functional components shown in FIG. 14;namely a knockout pin 100 disposed inside core 70 and an injectionnozzle 102 which is shown disposed inside a nozzle bushing 104. Withthese parts in place as shown, the mold is complete and raw moltenmaterial; typically HDPE, can then be injected through nozzle 102 intothe voids left between the mold components shown to thereby complete themolding of the filter 20.

[0049] Next, however, the filter must be removed from the mold. First,as the molten filter material begins to cool (cavity 80 can provide somepreliminary cooling), core 70 is removed from cavity 80 with the filter20 remaining on core 70. Knockout pin 100 is carried simultaneously withthe core 70 and filter 20 up and out of the cavity 80 during thisremoval step. Air may be forced up through the nozzle bore 106 into thecavity 80 against the header 30 to assist in this removal. Then, aftercore removal is complete, knockout pin 100 is forced through core 70 inthe relative downward direction of FIG. 14, while core 70 remainsstationary or continues on a relative upward track. This movement forcesheader 30 to move down and away from core 70 carrying the remainingintegral parts of filter 20 with it off core 70. It must here be notedthat if a substantially cylindrical or only slightly tapered design isdesired as is described here, then the choice of material used will beimportant as well. Specifically, a resilient (deformable, yetshape-retaining) material would be necessary to achieve the removal offilter 20 from the core 70 shown and described here, because the crossmembers 38, molded as shown, would need to deform outwardly from theirrespective notched voids in order to slide down and over thecorresponding exterior faces 84 of core 70.

[0050] Air may be forced downward between the core 70 and the filter 20to assist in this deformation for removal step. An exaggerated schematicillustrating this principle of deformation with the air assist is shownin FIG. 15. In particular, air would be forced into the circumferentialspace between the filter flange 26 and the core 70 as shown in FIG. 15.Then, the knockout pin (not shown in FIG. 15) can deliver its downwardforce and easily push the filter 20 off the core 70. A filter 20 wouldnot generally be expected to deform to the exaggerated extent shown inFIG. 15. Note, the header 30 is shown stretched in FIG. 15 to betterilluminate the overall deformation and resilience of a preferred filter20.

[0051] An alternative core shape is shown in FIG. 16 and is introducedat this point to illustrate a manufacturing difficulty inherenttherewith. A core 70A as shown in FIG. 16 has special notches 74A whichwould create the cross portions 38A shown in FIG. 16A. Cross portions38A present a nearly ideal shape because of the top and bottom decliningsurfaces 40A and 42A, respectively, which together would present verylittle inlet flow resistance. However. as shown in FIG. 16 during themanufacturing process, the introduction of air along the exteriorsurface of core 70A into what would be the corresponding space betweenthe core 70A and the filter 20A would not necessarily be sufficient todislodge the corresponding cross portions 38A from their respectivenotched voids because of the mold undercut portions numbered 75A in FIG.16. This makes molding this alternative embodiment difficult. Thedifficulties presented by mold undercuts in obstructing ejection areunderstood in the art. Nevertheless, the filter 20A embodiment is aneffective alternative for use according to the present invention.

[0052] As described above, the preferred method of manufacture involvesa two part, core and cavity, mold in which the core is inserted in thecavity to complete the mold. This is contrasted with a three part moldwhich could implement a core that is enclosable within a two partcavity. The two part cavity would come together about the core fromlateral directions. Thus, molds of this are commonly known as side-slidemolds. Use of a side-slide mold would present numerous distinctdisadvantages here. First, a side-slide mold has the inherentdisadvantage of the creation of flashing along the meeting edges of thetwo cavity parts. This flashing is extra molding material (HDPE, forinstance) which would adhere to the outside of the finished productafter the molding process. Large amounts of flashing would require anextra processing step for removing this material. Moreover, even ifthere is a minimal amount of flashing such that removal would bedifficult or ineffective, the flashing will nevertheless, present anunsmooth exterior surface for the filter which minimally presents anincreased flow resistance which maximally presents a risk of bloodcloning leading to the dangers addressed in the background sectionabove. The single mold cavity described above allows for a diamondpolished interior surface that yields an extremely smooth end productwith no flashing.

[0053] Moreover, the side-slide molding process traditionally involves asmooth core with mold voids created by notches formed on the interiorsurfaces of the two part cavities. Thus, a traditional side-slide moldformed to create the interior descending angled face 38 of the filter 20described herein would create an undercut mold feature which would makeremoval of the filter from the cavity very difficult. Indeed, the usualprocess for product removal in a side-slide is to first open the twocavity parts leaving the product on the core. However, with interiordeclining faces, lateral movement of the side cavity portions aftermolding would likely tear the product apart. The undercut mold portionswould effectively be fingers stuck into the finished filter which wouldgrip the filter thus disallowing a smooth lateral sideward slide. Thus,traditional side-slides involve only vertical, horizontal and exteriorangled surfaces such as that shown in Raabe (see FIG. 9, for example).Raabe presents no such side-slide difficulties; however, it thereforehas the perpendicular lower entry problem shown in FIG. 9.

[0054] Due also to the extremely close tolerances required by the coreand cavity relationship described herein, a further mold alignmentapproach was developed. In particular and as shown in FIGS. 17 and 18.one or more elongated trapezoidal ridges are formed in the mold base orbases to ensure alignment of the core and cavity. More specifically, andas shown in FIG. 17, a core 70 is disposed inside a cavity 80 in thesame fashion shown and described in FIG. 14. However, the respectivemold plates which house the core 70 and cavity 80 are also partiallyshown. Thus, a core plate 110 which houses core 70 is shown in crosssection. as is a cavity plate 112, which houses cavity 80. A base plate114 housing the nozzle bushing 104 is also shown. A male trapezoidalguide 120 is shown as an integral part of plate 110 as it has mated withthe female trapezoidal guide 122. As is understood in the art, plates112 and 114 are stationary (at least in the vertical direction relativeto FIG. 17), and plate 110 moves up and down carrying core 70 andknockout pin 100 with it during repetitive filter molding operations.Trapezoidal guides 120 and 122 are used to ensure that as core plate 110reaches its downward limit (with core 70 inserted in cavity 80), thecavity plate 112 and cavity 80 are fully and exactly aligned with core70 so that no physically damaging movement will result.

[0055] More specifically, the mold portion of core 70 is preferably afairly small member which must, during routine molding operations, beextensively reciprocated in and out of its corresponding cavity 80,always re-achieving a wall to wall contact relationship with cavity 80(with the exterior faces 84 of core 70 in full contact with the interiorsurface 82 of cavity 80). Thus, a high degree of physical stress can beimparted upon the core 70 by even the slightest degree of offset ofcavity 80 relative thereto. And, it is understood that in reciprocatinginjection molding apparatuses of the type described thusfar herein, oneportion of the mold will over time and usage, move. This may be due toexpansion caused by changes in temperature, or by other effects (theforces of injection will also impart deleterious stresses, bothlongitudinally and laterally). Usually, it will be the stationary moldplate, such as the cavity plate 112, here, which will accumulate thehigher degree of temperature change and thus expansion and relativemovement. Therefore, something other than the core 70 would need to movethe cavity plate 112 and cavity 80 back into proper molding position,and, a guide pin 124, as is known in the art, will be used herewith forthis purpose; however, guide pins, by themselves are not sufficient toabsorb the entirety of the expansion and other forces inherent over thewidth and length of the cavity plate. Therefore, the combination ofelongated longitudinal and latitudinal trapezoidal guide members (seeFIG. 18, as described below) is thought to provide greatertwo-dimensional lateral alignment.

[0056] Thus, as shown in FIG. 17, a male trapezoidal guide 120interlocked with a female trapezoidal guide 122 will serve to absorb thelargest share of any lateral expansion (or other forces) throughout therespective plates 110 and 112. Moreover, if made sufficiently deep. thatis. extending downward longer than core 70 (not shown in FIG. 17), then,the interlocking trapezoidal guide system could be used to perform thepre-alignment function that pin 124 (for example) provides. In this way,a male trapezoidal guide which is longer than a core 70 would, as coreplate 110 moves downward, then engage a female guide in cavity plate 112and thereby force cavity plate 112 into a properly aligned positionrelative to core plate 110, prior to the ingress of core 70 into cavity80. Similarly, plate 110 could be broken into two parts along the dashedline I in FIG. 17, such that the first part 110 could be made to comedown and force the interlocking mate relationship of guides 120 and 122prior to the downward movement of core 70 with the second part 110A ofthe core plate. This way, the alignment will be established prior toingress of core 70 into cavity 80.

[0057] Further, it is often desirable to mold a plurality of filterssimultaneously. A system for molding four such filters simultaneously isshown schematically in FIG. 18. There, a cavity plate 112 is shown withfour substantially identical cavities 80 and a female trapezoidal guide122 as described above. A further male trapezoidal guide is shown formedon this cavity plate 112. The alternation of male and female guides onthe same plate is primarily for tool manufacturing preference. It doesnot alter the operation as described. Rather, two female guides could beformed in one plate. as could two male guides formed in another plate;however. the formation of two male guides on one plate is problematicfrom a metallic tool shaping standpoint. Note, the trapezoidal guidesare preferably formed between the respective cavities and cores toenhance the stress distribution along the lengths and widths of therespective plates as described above.

[0058] The purpose, again, for these trapezoidal guides is to eliminatethe effects of any two dimensional, lateral (as opposed to longitudinal)stresses or movements of the cavity or cavities 80 in or with plate 112.Plate 112 is understood in the art to be a non-moving plate; however, itis also known that with continuous use, a non-moving metallic mold platewill heat up and will thus, naturally expand with the change intemperature (AT). The trapezoidal guides 120, 122 and 126. 128 areintended to alleviate the stresses and potential movements caused bythis heating.

[0059] Yet another related approach to curing this and similar alignmentissues is to make the vertically immobile cavity plate 112 twodimensionally floatable relative to plate 114. Thus, as set forth inFIG. 18, cavity plate 112 would be movable in the X-Z plane though stillnot vertically movable in the Y-dimension. Core plate 110 would remainnot movable in the X-Z plane, though still vertically movable (in theY-dimension). Consequently. when core plate 110 would come down forinsertion of core(s) 70 into the respective cavity (or cavities) 80,trapezoidal guides 120, 122 and 126, 128 would move the floating plate112 into place, and ensure core to cavity alignment. Here also, apre-alignment pin or pins (not shown in FIG. 18) such as pin 124 in FIG.17, could also be used for pre-alignment, or, interlocking guides 120,122, and 126, 128 could be used alone so long as they are sufficientlydeep to achieve contact prior to core 70 ingress into cavity 80.

[0060] One way to achieve the two dimensional floating of cavity plate112 as just described, is to attach plate 112 to plate 114 using one ormore shoulder bolt(s) 130 as shown in FIG. 17. Bolt 130 is shown firmlyaffixed in plate 112. but disposed in a sleeve 132 in nozzle plate 114.The firm attachment in plate 112 ensures no vertical movement (base 114is otherwise firmly affixed in space); however, the sleeve 132 providessome controlled lateral play. Thus. if over usage, the cavity plate 112or cavities 80 move at all, then the lateral play provided by sleeve 132allows for the trapezoidal guides to move the cavity plate 112 back toits aligned position for proper mating of cavities 80 with cores 70 formolding.

[0061] One further alternative of this floating approach is to severwhat was the previously integrated four part cavity plate shown in FIG.18, into four separate floating plates. This division could be madealong the trapezoid centerlines as shown by the dotted lines in FIG. 18.Thus. each cavity 80 in its respective plate portion may float relativeto each of the other cavities 80 and their respective plate portions,only to become properly aligned when the core plate 110 comes down tomate therewith. Still the trapezoidal guides 120, 122 and 126. 128 wouldpreferably do the moving to re-align the floating cavity plate portions.

[0062] Accordingly, a new and unique invention has been shown anddescribed herein which achieves its purposes in an unexpected fashion.Numerous alternative embodiments readily foreseeable by the skilledartisan, which were not explicitly described herein are consideredwithin the scope of the invention which is limited solely by the claimsappended hereto.

Accordingly, what is claimed is:
 1. A fluid filter comprising anelongated. substantially hollow body portion having an open base at oneend and a closed header portion at the other end; said body portionhaving a plurality of apertures formed therein, said apertures beingdefined side to side by elongated ribs running the length of the bodyportion, and top to bottom by cross portions having at least oneangularly declining, interior face.
 2. A filter according to claim 1 inwhich said at least one angularly declining face is a lower facedefining the bottom of the aperture.
 3. A filter according to claim 1 inwhich the exterior surface of said body portion is substantially smooth.4. A method for injection molding a filter having a plurality ofapertures, each aperture being defined in part by an interior decliningface, said method comprising the steps of: bringing a preselected coreinto position within a corresponding cavity to complete a mold;injecting a molten material into the completed mold; withdrawing thecore from the cavity with the molten material which remains adheredthereto in its molded shape; cooling the molten material to form apartially cooled filter; forcing air between the core and the partiallycooled filter; and knocking the partially cooled filter off the core. 5.A method according to claim 4 in which the cavity has a substantiallysmooth interior surface.
 6. A method according to claim 4 in which thecore is a substantially cylindrical member.
 7. A method according toclaim 4 in which the core has at least one elongated groove formedtherein.
 8. A method according to claim 4 in which the core has at leastone circumferential notch formed therein.
 9. A method according to claim8 in which each of the at least one circumferential notches has anangularly declining face which defines an angularly declining face in anentry aperture of said filter.
 10. A method according to claim 4 inwhich the molten material is a resilient plastic material.
 11. A methodaccording to claim 10 in which the plastic material is high-densitypolyethylene (HDPE).
 12. An injection molding apparatus for making afilter, said apparatus comprising: a longitudinally stationary moldcavity having a smooth, substantially cylindrical interior surface; anda longitudinally movable mold core having a substantially cylindricalmolding surface, said movable mold core being adapted to be disposed insaid mold cavity to form the filter mold; said molding surface of saidmovable mold core having at least one elongated groove and at least onecircumferential notch formed therein, said circumferential notch havingat least one angularly declining face; said movable mold core beingmovable into said mold cavity such that when fully disposed in said moldcavity, said molding surface of said core coacts with said interiorsurface of said cavity to complete the filter mold.
 13. An injectionmolding apparatus according to claim 12 in which said molding surface ofsaid movable core is adapted to engage the interior surface of said moldcavity in surface to surface sealing relationship with the exception ofsaid at least one groove and said at least one circumferential notch.said at least one groove and said at least one notch forming voidsbetween said molding surface of said core and said interior surface ofsaid cavity, said voids being adapted to be filled with and injectedmolten material during the injection process of molding.
 14. Aninjection molding apparatus according to claim 12 whereby said core isrepetitively moved into position within said cavity to complete themold; at which point a molten material is injected into the completedmold; whereupon the core is withdrawn from the cavity with the moltenmaterial beginning to cool and remaining adhered on said core in itsmolded shape to form a partially cooled filter; said partially cooledfilter then being stripped off said core.
 15. An apparatus according toclaim 12 in which each of the at least one circumferential notches hasan angularly declining face which defines an angularly declining face inan entry aperture of the filter to be formed.
 16. A method for injectionmolding a finished product comprising the steps of: having a cavityplate connected to a mold base in a laterally floating relationshipthereto, said cavity plate having a mold cavity disposed therein and anelongated trapezoidal guide groove formed therein; bringing a core platelongitudinally toward said cavity plate, said core plate having a moldcore disposed thereon, said mold core being adapted to be insertedlongitudinally in said mold cavity in said mold plate, said core platealso having an elongated trapezoidal guide ridge formed thereon, saidguide ridge being adapted to engage said guide groove in said cavityplate in an interlocking relationship; engaging said guide ridge on saidcore plate with said guide groove on said cavity plate in saidinterlocking relationship to align said cavity plate with said coreplate; engaging said mold core with said mold cavity to complete a mold;injecting molten material into said mold to form a molded product; andremoving said molded product from said apparatus.
 17. A method accordingto claim 16 in which the mold core is a notched and grooved member andthe mold cavity has a smooth interior surface, the mold core having atleast one exterior face thereof which meets with the interior surface ofthe mold cavity to define an aperture in the finished product.
 18. Anapparatus for injection molding a finished product, said apparatuscomprising a fixed nozzle base, a cavity plate which is attached to saidnozzle base in a two-dimensional, laterally floating relationshiprelative thereto, said nozzle plate having a female trapezoidal guideformed therein; and a longitudinally moving core plate which has a maletrapezoidal guide formed thereon, said male trapezoidal guide beingadapted to mate with said female trapezoidal guide to align the coreplate relative to the cavity plate prior to the injection moldingprocess.
 19. An apparatus for injection molding according to claim 18further comprising: a longitudinally stationary mold cavity disposed insaid cavity plate, said mold cavity having a smooth, substantiallycylindrical interior surface; and a longitudinally movable mold coredisposed in said core plate, said mold core having a substantiallycylindrical molding surface which is adapted to be disposed in saidcavity to form the filter mold; said molding surface of said mold corehaving at least one elongated groove and at least one circumferentialnotch formed therein, said circumferential notch having at least oneangularly declining face; said molding surface of said movable corebeing movable into said mold cavity such that when fully disposed insaid cavity, said molding portion and said cavity coact to complete thefilter mold.
 20. An injection molding apparatus according to claim 19 inwhich said molding surface of said movable core is adapted to engage theinterior surface of said mold cavity in surface to surface sealingrelationship with the exception of said at least one groove and said atleast one circumferential notch, said at least one groove and said atleast one notch forming voids between said core surface and said cavitysurface, said voids to be injected and filled with molten materialduring the injection process.
 21. An injection molding apparatusaccording to claim 19 whereby said core is repetitively moved intoposition within said cavity to complete the mold; at which point amolten material is injected into the completed mold; whereupon the coreis withdrawn from the cavity with the molten material beginning to cooland remaining adhered on said core in its molded shape to form apartially cooled filter; said partially cooled filter being stripped offsaid core.
 22. An apparatus according to claim 19 in which each of theat least one circumferential notches has an angularly declining facewhich defines an angularly declining face in an entry aperture of thefilter to be formed.